Exposure assessment of carbon nanotube manufacturing workplaces

Our plain-English summary of Exposure assessment of carbon nanotube manufacturing workplaces, by J.H. Lee, S.B. Lee, G.N. Bae, et al (Inhalation Toxicology, 2010).

The study

• Authors: J.H. Lee, S.B. Lee, G.N. Bae, K.S. Jeon, J.U. Yoon, J.H. Ji, J.H. Sung, B.G. Lee, J.H. Lee, J.S. Yang, H.Y. Kim, C.S. Kang, I.J. Yu
• Journal: Inhalation Toxicology
• Published: 2010;22(5):369-81
• Cited by: 100 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Seven CNT (carbon nanotube) handling workplaces were investigated for exposure assessment. Personal sampling, area sampling, and real-time monitoring using an SMPS (scanning mobility particle sizer), dust monitor, and aethalometer were performed to characterize the mass exposure, particle size distribution, and particle number exposure. No workplace was found to exceed the current ACGIH (American Conference of Governmental Industrial Hygienists) TLVs (threshold limit values) and OELs (occupational exposure levels) set by the Korean Ministry of Labor for carbon black (3.5 mg/m(3)), PNOS (particles not otherwise specified; 3 mg/m(3)), and asbestos (0.1 fiber/cc). Nanoparticles and fine particles were most frequently released after opening the CVD (chemical vapor deposition) cover, followed by catalyst preparation. Other work processes that prompted nanoparticle release included spraying, CNT preparation, ultrasonic dispersion, wafer heating, and opening the water bath cover. All these operation processes could be effectively controlled with the implementation of exposure mitigation, such as engineering control, except at one workplace where only natural ventilation was used.

In plain English

This study measured airborne particles at seven Korean workplaces that made or used carbon nanotubes, mostly multi-walled carbon nanotubes (MWCNTs), from July to September 2008. The study concerned carbon nanotubes, not asbestos; it used the asbestos exposure limit as a comparison. The workplaces were industrial plants, research institutes and laboratories. The authors used personal and area filter sampling, electron microscopy to look for tube structures, and real-time particle counting and sizing instruments. Total suspended particle levels ranged from 0.0078 to 0.3208 mg/m3 in personal samples and from 0.0126 to 0.1873 mg/m3 in area samples. The authors reported that no workplace exceeded the limits for carbon black (3.5 mg/m3), particles not otherwise specified (3 mg/m3) or asbestos (0.1 fiber/cc). One area sample showed MWCNT tube structures at 0.00312 tubes/cc. Opening the chemical vapor deposition (CVD) reactor most often released nanoparticles, followed by catalyst preparation. The authors considered the particles released on opening the reactor to be mainly metal catalyst. The authors concluded that these processes could be effectively controlled by measures such as engineering controls, except at one workplace using only natural ventilation.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Cross-sectional workplace exposure assessment (air sampling and real-time particle monitoring)
• Who was studied: Seven workplaces handling carbon nanotubes in Korea, measured July to September 2008. Three were industrial plants (A, B, C), two were research institutes (D, E) and two were laboratories (F, G). Each site had 3 to 5 handling workers.
• Exposure: Airborne particles from manufacturing or applying multi-walled carbon nanotubes (MWCNTs). Processes included CVD synthesis, catalyst preparation, spraying, ultrasonic dispersion and wafer heating. Some application sites were research institutions.
• Main results:
  • Total suspended particulate matter ranged from 0.0078 to 0.3208 mg/m3 in personal samples and from 0.0126 to 0.1873 mg/m3 in area samples.
  • No workplace exceeded the ACGIH TLVs or the Korean Ministry of Labor OELs for carbon black (3.5 mg/m3), PNOS (3 mg/m3) or asbestos (0.1 fiber/cc).
  • One area filter sample at workplace C (area 6) showed MWCNT tube structures at 0.00312 tubes/cc. The article's tables list the other filter samples as not detected.
  • Opening the CVD reactor gave the most frequent nanoparticle release, followed by catalyst preparation. Table 11 counts 4 releases for CVD opening and 2 for catalyst preparation (N = 7).
  • The authors considered the particles released on opening the CVD reactor to be mainly metal catalysts rather than MWCNTs.
  • During catalyst preparation, the geometric mean nanoparticle count (SMPS) was 37,350 particles/cm3, with a range of 18,600 to 75,000.
  • On CVD opening, the geometric mean nanoparticle count was 11,039 particles/cm3, with a range of 6,974 to 16,857. Table 12 prints this value as 11,030.
  • Ultrasonic dispersion released larger particles, mainly 120 to 300 nm in size.
  • By mass, most workers were exposed far below the ACGIH carbon black limit.
• The authors' conclusion: The authors concluded that the particle-releasing processes could be effectively controlled with exposure mitigation such as engineering control. The exception was one workplace that used only natural ventilation.
• Limitations the authors state:
  • In some cases CNT tube structures could not be counted. The authors offered possible reasons, including clumping, no release, or improper sampling.
  • Background measurements before work were short and were done only at workplaces D and E.
  • Exact exposure assessment methods for nanoparticles have not yet been established.
  • Further studies on CNT sampling and exposure are needed.

Topics

Medical terms in this study, explained in our Lexicon: Threshold Limit Value (TLV), Occupational Exposure, Deposition.

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